An optical disc is a high-density information recording medium in which information is recorded by using a semiconductor laser and is reproduced by using the difference in the reflectance of light beams between a recorded part and an unrecorded part.
The optical disc is provided with one or a plurality of “recorded area(s)” in which a predetermined information signal is written. “An unrecorded area” in which a new information signal can be written is provided outside the recorded area. In particular, in order to reproduce an optical disc on which recording has been performed several times, it is necessary to know the number of the recorded areas of the disc. In other words, it is necessary to detect “the last recorded area” of the disc to be reproduced. In this way, in order to detect the last recorded area of the disc to be reproduced, it is necessary to access the recorded areas sequentially from the first recorded area by moving the optical head repeatedly. However, it is impossible to know whether a succeeding recorded area exists or not before the optical head is moved to the position, and when the optical head is moved to an unrecorded area, servo control cannot be performed, thus bringing about an abnormal state.
Therefore, in a reproducing method for an optical disc described in Published Unexamined (Kokai) Japanese Patent Application No. Hei 6-349252, an address of a lead-out area is readded at a lead-in area provided in the first position of the recorded area, and then this lead-out area is accessed. Next, an optical head is moved to the succeeding recorded area by repeating one or more jump of one track or a plurality of tracks in the direction to the outer circumference. When it is decided that the optical head reaches the unrecorded area, the optical head is returned toward the inner circumference side without turning on the tracking servo. According to this method, an abnormal state due to the disability of the servo control is prevented.
However, in the reproducing method for the optical disc described in the above-mentioned publication, the optical head cannot be prevented from reaching the unrecorded area in detecting “the last recorded area.” Therefore, it becomes necessary to perform an operation of returning the optical head toward the inner circumference side without turning on the tracking servo. Thus, “the last recorded area” cannot be detected efficiently.
Recently, a technique is suggested, in which a recognition mark area for recognizing whether the succeeding area is an unrecorded area or not is provided just behind the last data in the recorded area, and the state of the recognition mark area is detected by the behavior when the recognition mark area is accessed, thereby determining whether the area behind the recognition mark area is an unrecorded area or a recorded area (whether the recorded area is the last recorded area or not). In this technique, when the recognition mark area cannot normally be accessed, the succeeding area is determinined to be the unrecorded area. In this case, when the recognition mark area is accessed, first, the lead-in data at the head of the recorded area is accessed so as to obtain the address of the lead-out area, and then the address of the recognition mark area existing in the vicinity of the head of the lead-out area is accessed. When a new information signal is written in the unrecorded area, a reproducible recording mark that does not cause a data error is recorded in the recognition mark area, and at the same time a new recognition mark area is provided behind the area in which the new information signal is written (the new recorded area).
However, in the above-mentioned marking method, when the recognition mark area is provided just behind the last data in the recorded area, if an access error exists when the last data in the recorded area is accessed, the optical head wrongly jumps to the recognition mark area, which may lead to an unstable access operation. Furthermore, when the recognition mark area is provided just before the unrecorded area, the optical head jumps to the unrecorded area at the time of accessing the recognition mark area, thus bringing about an abnormal state due to the disability of the servo control. In addition, if a succeeding recorded area exists, when the first data in the succeeding recorded area is accessed, the optical head jumps to the recognition mark area, thus bringing about an unstable access operation.